This invention relates to the foundry art, and, in particular to a sand binder system utilizing furfuryl alcohol monomer.
Generally speaking, the so-called furane foundry binders have been produced from partially resinified mixtures involving furfuryl alcohol, and sometimes including furfural, urea, formaldehyde, phenol and the like.
For the purposes of providing background of the present invention, the furane binders can be regarded as being categorized in one of three classes; namely, the cooked type, (monomeric), polymeric, and the phenol-containing type. The first type of furane binders generally involves mixing monomeric furfuryl alcohol, urea, and formaldehyde, with adjustment of pH to 4.5 or higher, and cooking the resulting mixture for two hours, for example, at an elevated temperature such as 100.degree. C. Under these conditions the furfuryl alcohol polymerization is minimal but the conditions do provide for incorporation of the furfuryl alcohol monomer by condensation into a resin with the urea and formaldehyde.
The so-called polymeric type binder involves the admixture of furfuryl alcohol monomer with urea and/or urea formaldehyde with the adjustment of pH to well below 4.5, e.g., 2.0, and cooking to a desired viscosity for example at 100.degree. C. Ordinarily the water of condensation is stripped off under reduced pressure and the resulting polymer is quite viscous. The resulting polymer is then typically diluted with furfuryl alcohol monomer or in some cases with furfural to get a desired viscosity.
The third type of furane binder involves pre-condensation with phenol, and, typically, the phenol is first polymerized with formaldehyde, for example, under alkaline condition, and the resulting phenol aldehyde is reacted or admixed with furfuryl alcohol polymer typically furfuryl alcohol formaldehyde or furfuryl alcohol urea formaldehyde polymer prior to admixture with sand, for example.
Illustrative of the furfuryl alcohol-phenol resin art are U.S. Pat. Nos. 2,470,440 to Joseph N. Kuzmick, 3,299,167 to Paul E. Knowlson, et al., 3,716,512 to Silvio Vargui, et al., 3,793,286 to Kenneth C. Petersen, et al., 3,847,860 to Claus-Dieter Seiler et al., Netherlands Patent Application No. 66-08856 by Archer Daniels Midland Company, and British Patent Specification No. 1,012,067 to Dow Chemical Company.
Of particular interest is U.S. Pat. No. 2,848,430 to R. N. Frey, et al., which relates to tall oil-phenol furan resin compositions. Whereas the other patents involve the pre-condensation of phenol with various materials, the Frey patent contemplates the use of a monomeric phenol with furfuryl alcohol-tall oil as a phenol-furan resin. Although most of the phenolic compounds discussed by Frey were monohydric, Frey does refer to the use of dihydroxybenzene such as resorcinol. It is noted that FIG. 2 of Frey shows a mixture of tall oil, phenol, and furfuryl alcohol in a number of compositions illustrated in the three sided graph, and a series of compositions drawn along the bottom line of the graph illustrates a range of mixtures of phenol and furfuryl alcohol having between 35 and 60 percent phenol.
At column 2, line 26 Frey makes the statement that from the variety of substituted phenols that were tried, the addition of tall oil to the basic phenol-furan system in no way materially affected the chemical reaction. On the other hand, in Example 7, Frey illustrates the efficacy of both catechol and resorcinol, and it is unequivocally stated "that only the catechol produced the thermosetting resin when combined in a 1:1:1 ratio, by weight with furfural and tall oil. The resorcinol did not react in the 1:1:1 ratio to produce the thermosetting resin with either the furfural or the furfuryl alcohol. Catechol, on the other hand, did produce the resin with furfural, but not with the furfuryl alcohol".
Contrary to the express teachings of Frey, however, we have discovered that a monomeric mixture of resorcinol and furfuryl alcohol is extremely useful as an acid catalyzable liquid binder for the purpose of producing foundry sand shapes.